Our spy photographers have spotted the new Fiat 124 Spider out during testing in North America.

The new Fiat roadster is based on the fourth-generation Mazda MX-5. While the two will share a chassis and underlying body structure, the two will differ in terms of the drivetrains offered.

Stylistically, these photos also indicate that Fiat's version will feature new external body panels. Up front, the 124 has larger round headlights and a complex grille treatment.

From the side, the Fiat 124 looks as though it may also feature a subtly different shoulder line. At the rear, the Fiat sports larger tail-lights, a different boot lid with lip-mounted third brake light, and rearranged exhaust tips.

Reports indicate that the base Fiat 124 Spider will be equipped with a 1.4-litre turbocharged motor. A sportier Abarth version is also being planned and this model will use the 1.75-litre turbo engine currently employed in the Alfa Romeo 4C.

UPDATE: the 124 Spider has now been spied without camouflage. Read here.

This contrasts with the 1.5-litre four-cylinder base engine and the more powerful 2.0-litre motor used in the MX-5, both of which are naturally aspirated.